Work holding chuck



Jan. 1W, W5

Filed Aug. 13, 1954 G. F. BREWSTER ZJBQBW WORK HOLDING CHUCK 2 Sheets-Sheet l INVENTOR. .5 BY MM FEW WM ATTORNEY Jan. 10, 1956 F. BREWSTER WORK HOLDING CHUCK 2 Sheets-Sheet 2 Filed Aug. 13, 1954 FIG.9

FIG.8

FIG.7

m m m m ATTORNEY FIG. 10

United States Patent WORK HOLDING CHUCK George F. Brewster, Kittery, Maine M J Application August 13, 1954, Serial minaret 9 Claims. cl. 219+ This invention relates to an improved work holding chuck of the. vacuum-operated type for use in holding surfaces of work pieces which .areto be subjected to 2,730,370 te e Jef- 9: 1??

'ice

Fig 9 is aviewin elevation illustrating a length been:

ing ring material suitable "for beingcut-into desired 'sea'iin'i ring diameters; and

Figll) is another modified chuck arrangemento the invention. 1

I. have discovered that the suction-induced holding some.

normally developed-in a conventional-type'of vacuuni operated chuck may be combinedwithcerta'in forcesj-de veloped in stretching an elastic-body with the 'r'sult that I am. enabled to provide for holding work pieces in] a manner not heretofore realized in the art and, as a result 1 ofvwhich, unusual and surprising advantages" are realized;

utilization is prohibitive in a great'many instances, -par-' ticu'larly"where it may be desired to hold relatively small work pieces for fine machining operations and where" the surfaces of such small work pieces may be rough orcharacterized by small irregularities. I The present invention is concerned 'withtlie proble indicated and aims to provide an improved method and apparatus of the vacuum-operated type for holdiiiQwork pieces.- It is especially an object or the invention to devise means for sharply increasing the holdin'g 'elfect which can be realized with a vacuum-operated type of chuck, which means is capable of embodimentina'wide range of holding devices and which may be applicable tornany different kinds of work pieces in'various work ing operations involving machine tools or other pro cedures. These and other objects and novel features will be more fully understood and appreciated from the following de scription of a preferred embodiment of the invention 'selected for purposes of illustration and shown in the accompanying drawings, inwhich I "j H Fig. "1 is a fragmentary crosssectional vie'w shdwi ngl a simplified form of work holding chuck and sealing means of the invention with a work piece having been indicated in broken lines ina position normally assuinediby "the workpiece just prior to its being brought into engagement withthe work piece holder; jj i I "Fig-1 2 is another fragmentary cross-sectional view of the structure shown in Fig. 1 but further illustrating the work piece. in a. fully engaged position on the work holder chuck;

Fig. 3 is an elevational view of the sealing ring shownin Figs. 1 and 2'and also indicating in broken linesthe position assumed by this member when caused toflrnovev into a circumferentially extended shape; V Fig 4 isa fragmentary cross sectional. .viewof amedb, fi ed form of work holding chuck; p Q I Fig. 5 is a view in elevation of another form of work' holding chuck illustrating a multiple work holding 'sur-' face arrangement, together with special clamping means; Fig. 6 is a cross-section taken on the line 6-'-6' oi 5.; v Fig.1 7i's' a detail fragmentary view of thestructure ShOWILiIl Figs. Sand 6; II Fig. 8- is acrossrsecti'onal view-of a sealingring-materiah employed? in: the; invention; II I I I have found that, in exerting a suction forcci to draws work piece against the 'face of a vacuum type-chuck}! may introduce between'the face'and work piece a special typeof elastic sealing member. This sealing-member is,

. in accordance with the invention, located in-a *p'ositibi'r become deformed and such-that it may be'caused to cir'cumferentially stretched into a shape in which it coiif tinually exerts a force of contraction. U

I find that this force of contraction properly induced and applied constitutes an independent means of'pro ducing a seal between portions of the stretched sealing member and its respective seating surface to the me that this force of contraction cooperates with the conventiona'i suction force and greatly increases 'the' over-all holding power of the chuck. I

" Inthis connection, -I have devised a chuck body mi struciedwith 'a special: ring seating surface which is'char acterized by :a varying-circumferenceand I havefurtheri devised, for use with this ring seating surface, an-elastic ring body oftoric section whose size and compressibility characteristics are so chosen that the ring may be c'orivenientl-y rec'eived'in a position inwhich it normally projects out of the plane of the faceof the chuck body." By means of this arrangement, the projectin'g'p'ortion ofthe sealing ring may be engaged by the work piece coming into contact with the face of the chuck and the"ring*'a's' a whole is simultaneously compressed, fiattened'outand" caused tob'ecome circumferentially stretched;

- A preferred embodiment of the ring'seating surface-for achieving these results ma I find, comprise a hyper boioidal surface whose diameter, measured at points com tactedby the ring in a corn-pressed state, is greater than theinner diameter of-=this ring to the endthat the ring, when fully compressed into a flattened out positiorifis' stretched circumferentially in a degree sufiicient tode velop an appreciable force of contraction acting iri' a radially 1 inwardly directed manner all around the hypers boloida'l surface. Y:

In: conjunction With-this force of contraction acti I .e in'the manner described, it is pointed'out-Ethat the flatten-"'- ing out of the sealing ring by the work piece'produt's" anxincrease in the 'aict'uah'area' of contactofF'the ring against its seating surface so that the. force of co'ntrac tion has an opportunity to act over a relatively largerarea which aids materially in sealing a rough or warped surface.

In the. structure'shown in"th'c drawings, Figs. Panda. 2 illustrate a" simplified form of-wor'k holding chuck sti tunn'g one preferred embodiment (tithe-invention; I A's I noted'there'in, numeral Zdenotes'a vacuum-operated typ chuck body for use'in-holdinga-work' piece W in posi tion 'to undergo various machine operations ofwelt; known type. The chuck body is recessed to form arrah conduit 4 through which air may be exhausted by-mea'n's of any-conventional suction-pumpingmechanism: 7 The showing in the drawings of an air conduit 4 isii-itended torbe indicative of.- a. complete. suction mechanism of conventional-nature no further-showing ctr-aside: tionalsnctioncomponents is believedstobernecessasyim I the drawings.

= .t-urn eifect useful for ven't ional mode of operation of such a vacuumoperated device is to locate a work piece against the face of the chuck and then remove air from betweenthe members, thereby enabling atmospheric pressure to hold the parts against one another. It is pointed outthat the degree of holding strength thus conventionally developed is dependent very largely upon the effectiveness of the seal which can be, obtained to prevent outside air from passing in between the surfaces. In practice, maintenance of a, seal is a very troublesome problem, particularly in dealing with rough or grained surfaces on: work pieces, since the sealing action induced by the suction forces available are not always adequate to force the sealing into sufficiently intimate contact with all of the minute depressions and irregularities which may be presentin the surface of the work piece. l

In accordance with the invention, 1 provide for formigg a seal whichovercomes these dilficulties by employ.-

inga sealing ring 7 comprised of an .elastic material,

such as-rubber, plastic, or the like, and constructed of toric cross-section such as is commonly represented by the article sold in the trade as an O ring.. This sealing ring I mount-on a work holding element or boss 6 which preferably is constructed at its top with a fiat engaging face 8. Formed around this boss 6 is a specially devised ring sealing surface 10 of the invention, which surface is of varying circumferential characteristics and which, in a preferred form, consists of a double-curvedsurface formed by moving a curved line of generally hyperbolic shape about a vertical axis to define a hyperboloidal body. The dimensional characteristics of this hyperboloidal body are ;chos en such that the diameter of the hyperboloidal body, ,at points therein, is greater than the diameter of the sealing ring and increasesprogressively, as best shown in Figs'l and 2. H. I

In the preferred form of holder shown in Figs. 1 and 2, the structure described results in the formation of a lip portion 12 which has -a diameter slightly greater than the inner diameter of the sealing ring andthe lip may thus-operatefto retain the ring on the work holder elementin all positions of use in which it may be disposed.

The change in shape and circumference of the sealing ring 7, resulting from drawing the workpiece W into contact with the work holder surface, may be more clearly seen from an inspection of Figs. 1 and 2 wherein the arrow A de notes the diametervof, the ring before iAsji s well known to those skilled in the the con:

which isv provided a ring 17 on a ring seating surface. 18

of the character already described. Such an arrangement is intended'to be employed in holding work pieces or other articles having surfaces which are curved.

In Figs. 5, 6 and 7, I have illustrated another form of work holder 20 in which are formed a number of concentric grooves, as 22, 24, 26 and 28, which define a series of progressively larger work holding elements, as 21, 23, 25 and 27. All of these work holding elements are constructed with hyperboloidal ring retaining surfaces of the invention and may support sealing rings as 30, 32, 34 and 36, used either separately or in conjunction with one another. A feature of this construction is the provision in each of the work holding elements, 21, 23, and 27, of holes, as 31, 33, 35 and 37, in which may be engaged screwsQas 40, to hold clamps 42, 44, 46 and 48. The lattermembers may be placed at any desired points on the respective holding elements to hold a work piece against displacement from laterally directed forces which might operate to slide the work piece sideways and thus break the seal. The various sealing rings in any of the grooves will normally extend upwardly, as shown in Fig, 7.

I In- Fig. 8, I have illustrated the use of elastic material R in varying lengths so that, for any desired diameter of ring required, for example in the multiple face chuck body 20, Lmay cut off a piece of stock, as shown in Fig. 9,

, cement the ends of this piece together and install.

I may also desire to use a sealing ring with a hyperboloidal seat in-connection with a recessed chuck of the type shown in Fig. 10 to obtain a large vacuum pocket from which air is exhausted. This numeral denotes a chuck body formed with an air passage 64 which communicates with the opening defined by the recessed surface 66. A ring 62 engages this chuck body around its sealing surface of the same general type described.

It will be seen that I have thus devised an improved method and apparatus for producing a vacuum-operated sealing effect which may be applied, particularly in refer-. ence to holding work pieces on a chuck member but which may also be used, generally, wherever aholding operation is required, and it is possible to remove air from between the work holding element and a surface to be engaged stretching arrow B indicates the diameter. after stretching. This change in dimension is also illustrated byFig.3.

Attention is also directed tothe fact that, the actual area of. contac t of the ring with its seating surface, as shown in Fig. 2, is nearly twice as largeas the area of contact shownin Fig. l which, obviously, is a material aid to increasing the desirable sealing action of the ring against its hyperboloidal seat.

Although I have in mind using the toric sealing ring and special seating surface described in ,many cases in conjunction with a suction-pumping mechanism, I do not wish to limit my invention to such an arrangement or method and I may, on the contrary, desire to utilize the partsdescribed as an independent work holding device used by itself. In this connection, it is pointed out that the unexpectedlystrong sealing action which is derived thereagainst.

While I have shown and described preferred embodiments of the invention, it should be understood that various other changes and modifications may be resorted to in accordance with the scope of the appended claims.

. I claim:

'1. In a vacuum-operated chuck for holding a work piece, a work holding element, an elastic sealing ring, a ring seating surface formed on said work holding element and normally adapted to receive and support the sealing ring in a position in which it projects beyond one side of the holding element, and said ring seating surface being formed with a groove having a hyperboloidal surface for causing the ring to move intoa circumferentially extendirig position when the said work piece is forced into contact with the work holding element.

2. In a vacuum-operated type chuck for holding a work piece, a work holding element including suction means for holding a surface of the work piece thereagainst by atmospheric pressure, an elastic sealing ring, said work holding element being recessed to define a groove having thereby produce a limited vacua hyperboloidal cross-section for receiving said sealing ring and normally supporting it in a position in which portions of the ring project beyond the work holding element, the diameter of the groove at some points exceedingthe inner diameter of the sealing ring.

i 3. An improved work piece chuck comprising'a work holding element having a ring groove formed therein, a sealing ring mounted in the groove of the work holding element, said groove presenting a hyperboloidal surface,

' and lip meansformed on the work holding element for maintaining the ring in a seated position .and being co-- extensive with and constituting one boundary edge of the said hyperboloidal surface.

4. A structure according to claim 1 in which the work holding element presents a flat face having a plurality of concentrically arranged ring grooves formed therein.

5. A structure according to claim 1 in which the work holding element presents a curved face.

6. A structure according to claim 1 in which the chuck includes a plurality of work holding bosses arranged in concentric relationship to one another, and a plurality of sealing rings secured around said bosses on respective double curved ring supporting surfaces.

7. A structure according to claim 1 in which the work holding chuck includes a plurality of work holding bosses arranged in concentric relationship, and clamping means 15 2,443,987

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for engaging a work piece while supported on one of the Work holding bosses.

8. A structure according to claim 1 in which the hyperboloidal surface terminates in a lip of a diameter slightly greater than the inner diameter of a sealing ring, said hyperboloidal surface extending in a direction away from the said lip with a gradually increasing diameter exceeding the inner diameter of the sealing member.

9. A structure according to claim 2 in which the face of the said chuck is recessed.

References Cited in the file of this patent UNITED STATES PATENTS Petry Apr. 23, 1946 Morrison et al. June 22, 1948 

